The present invention relates to a vehicle system and an earth-based receiver system for controlling operating states of a vehicle system or of a vehicle on the basis of satellite signals, using an estimation of error from received satellite signals.
Systems for determining the integrity of position solutions derived from satellite signals are known from the prior art. It is assumed that, after application of a correction to the satellite data made by an optional base system, all satellite signals that are not recognized as erroneous by the earth-based receiver system may be described by an error distribution, and that the signals have an expected value of zero and may be described by a standard deviation.
Such a system is known from European patent document EP 04 022 307.5, for which it is assumed that there are a plurality of satellite signals that are applicable for this assumption, but that for each vehicle system there is a satellite signal having the associated data for which this assumption is not applicable. For this satellite signal and the associated data it is then assumed that for the satellite in the earth-based receiver system the expected value of the error distribution is the threshold value that is propagated for this satellite, and that the variance of the error is the variance of the error estimation which is propagated by the receiver system.
The object of the present invention is to provide a system which allows the integrity of position solutions derived from satellite signals to be determined with greater reliability and lower alert limits.
According to the present invention, a vehicle system in a vehicle includes a position determination module for determining the position of the vehicle using an estimation of the error of satellite signals which are received by an earth-based receiver system, and an integrity module for determining an integrity risk for the position data for a vehicle. The integrity risk is derived using time determinations performed by a satellite navigation system, and when a threshold value for the integrity risk for the position data is exceeded, the vehicle system generates a warning signal which, by means of modules that are connected to the vehicle system, is designed to prevent the use of the position data for the vehicle, wherein the integrity risk is determined using an estimated value for the error in the received satellite signal,                wherein only satellite signals and satellite data, and optionally correction data, are used which as a whole have not been transmitted by the earth-based receiver system to the vehicle system as erroneous,        wherein this estimated value is set to be equal to the received threshold value,        wherein optionally the algebraic signs of these estimated values are selected so as to maximize the integrity risk, and        wherein the accuracy of this estimated value is set to be equal to the deviation accuracy transmitted from the receiver system to the vehicle system.        
Also provided according to the invention is a receiver system which functionally interacts with a plurality of satellites to determine and transmit data to a vehicle system containing a position determination module for determining the position of the vehicle, and an integrity module for determining the probability that the position error is greater than an alert limit, whereby the receiver determines:                the position and the instantaneous time of the transmitting satellite,        the deviation between the satellite position and satellite time predicted for the particular point in time and the estimated satellite position and satellite time,        the deviation between the nominal signal propagation from the satellite to the vehicle and the estimated actual signal propagation from the satellite to the vehicle,        the deviation accuracy, i.e., the accuracy with which this deviation is determined,        a threshold value above which the receiver system identifies the respective satellite signal received by same as erroneous, and        the information concerning which satellites are recognized as defective by the receiver system,wherein the receiver system transmits the following as input data for the vehicle system:        the accuracy of the error estimation, and        the information concerning which satellites are recognized as defective by the receiver system,wherein the receiver system also transmits as input data for the vehicle system a threshold value above which the receiver system identifies the respective satellite signal received by same as erroneous.        
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.